(1) Technological Field
The present invention relates to an optical print head (PH) and an image forming device.
(2) Description of the Related Art
According to recent image forming devices employing an electronic photography system, organic light emitting diode print heads (OLED-PHs) reducible in size and cost, which serve as optical PHs for exposing a photoreceptor to form electrostatic latent images, are under technical development. Manufacturing cost of OLED-PHs can be reduced by integrally forming OLEDs on a thin film transistor (TFT) substrate.
In an OLED-PH, OLEDs are arranged in a line-shaped region in a main scanning direction, and driving circuits are also arranged in a line-shaped region in the main scanning direction. The driving circuits are disposed close to the respective OLEDs, and control light emission amounts of the respective OLEDs. Meanwhile, a drive integrated circuit (IC) and a power source terminal are provided on one end of the OLED-PH in a longitudinal direction thereof. The drive IC receives image data from a main body of an image forming device, and inputs light amount control signals designating light emission amounts of the OLEDs to the respective driving circuits. The power source terminal is for power supply to the OLED-PH. Due to this configuration, signal wirings and source wirings from the drive IC and the power source terminal to the driving circuits are elongated.
Intersection between such wirings generates a parasitic capacitance at an intersection part therebetween. For example, intersection between a signal wiring and a source wiring causes a parasitic capacitance to act as a coupling capacitance. When a light amount control signal switches on and off on the signal wiring, a noise is superimposed on the source wiring. This varies a drive current for supply to the OLEDs and varies a light emission amount of the OLEDs accordingly. As a result, image quality might be deteriorated.
In response to such a problem, an art has been proposed for example of disposing an inverter on a signal wiring in units of blocks each including OLEDs, such that a logical level of a light amount control signal on the signal wiring is inverted at an intersection part between the signal wiring and a source wiring (see for example JP2008-117882). According to this art, noises superimposed on the source wirings after inversion cancel each other at intersection parts. This suppresses variation of the source voltage, thus suppressing image quality deterioration.
However, it is sometimes impossible to invert polarity of noises superimposed on wirings for mutual cancellation. For example, around a photosensitive drum for electrostatic latent image formation, a charging device and a developing device, which generate a high frequency noise, are provided in addition to an optical PH. Superimposed high frequency noises vary a light amount control signal and this causes a stripe density unevenness in an image. Unfortunately, because of impossibility of inversion of the polarity of high frequency noises, it is difficult to apply such a conventional art as above to suppress image deterioration.